In manufacturing a metal oxide TFT, six photolithographic processes each consisting of masking, light exposure and etching are required to form the metal oxide TFT, which include to form the gate electrode, the metal oxide (channel) layer, the etch stop layer, the source and drain electrodes, the through holes in an insulating layer over the source and drain electrodes and the pixel electrodes over the insulating layer. The six masking steps of the six photolithographic processes are expensive and complicated.
Furthermore, the TFT made by the method having such numerous masking steps has a poor dimensional precision, since each masking step needs to align the mask with the TFT, which unavoidably results in a tolerance. The disadvantage of the poor dimensional precision becomes more unfavorable in view of the current trend of high definition display.